In a manufacturing process of a semiconductor device, a prescribed circuit pattern is formed on the surface of a semiconductor wafer by using a so-called “photolithography technology”. In the photolithography step, a series of treatments are carried out such that a resist film is formed on a cleaned semiconductor wafer by supplying a photoresist solution onto the semiconductor wafer, followed by exposing the resist film to light in a prescribed pattern and subsequently developing the pattern.
In the developing step, an exposed semiconductor wafer is held first by a rotatable spin chuck. Then, a puddle of a developing solution is formed by supplying a developing solution onto the surface of a semiconductor wafer held by the spin chuck, and the developing solution supplied onto the surface of the semiconductor wafer is left to stand for a prescribed time so as to permit the developing reaction to proceed. In the next step, a rinsing liquid such as pure water is supplied onto the semiconductor wafer while rotating the semiconductor wafer so as to rinse the semiconductor wafer. Finally, the supply of the rinsing liquid onto the semiconductor wafer is stopped, and the semiconductor wafer is rotated at a high speed so as to dry the semiconductor wafer by spin-drying in this case, a tetramethylammonium hydroxide (TMAH) solution having a fixed concentration of, for example, 2.38% by weight is used as the developing solution for the various resist materials.
It was possible in the past to obtain the required defect control with the standard process. In recent years, however, light having a shorter wavelength has come to be used for the exposure, and the pattern exposed and constructed by the light has been made finer and finer. Under these circumstances, it is difficult to form a defect-free circuit pattern by the conventional method for the developing process.
A significant mechanism for defect formation is the relation between the physical properties of the current photoresist materials and the current developing materials. The photoresist materials exhibit low surface energy, and the liquid developing materials exhibit high surface tension. This combination results in a high contact angle between the photoresist surface and the spreading developing liquid. This high contact angle opposes uniform spreading of the developing liquid and can cause the liquid to capture small air bubbles (microbubbles). It can also increase capture of defect-causing particulates that may be on the surface.
Several approaches have been tried to reduce this defect-causing event. For example, surfactants have been added to the developing materials to reduce the contact angle of the spreading developing liquid. In other examples, complex mechanisms have been invented to apply the developing liquid with unique nozzle configurations and spinning wafer application. These approaches have had limited success. Adding surfactant to the developing liquid itself affects the developing characteristics. The complex mechanisms and spin/dispense recipes are difficult to program and control repeatably, and they do not resolve the fundamental problem of high contact angle.